Question

I have two dataframes

df1 = data.frame(Sites=c("A","B","C"),total=c(12,6,35))

df2 = data.frame(Site.1=c("A","A","B"),Site.2=c("B","C","C"), Score=c(60,70,80))

I need to merge them to produce the dataframe

df3=data.frame(Site.1=c("A","A","B"),Site.2=c("B","C","C"),
Score=c(60,70,80),Site.1.total=c(12,12,6),Site.2.total=c(6,35,35))

Any advice on the simplest way to do such a double merge? Thanks

Answer 1

Simply merge twice:

x <- merge(df2, df1, all.x=TRUE, by.x="Site.2", by.y="Sites", sort=FALSE)
merge(x, df1, all.x=TRUE, by.x="Site.1", by.y="Sites", sort=FALSE)

  Site.1 Site.2 Score total.x total.y
1      A      B    60       6      12
2      A      C    70      35      12
3      B      C    80      35       6